This invention relates in general to the field of electromagnetic signal generating sources, in particular to frequency stabilization of sources, and, more particularly, to passive frequency stabilization of high power microwave sources.
Frequency stabilization of sources is important for many electronic products which require highly stable free-running oscillators. Microwave signal generating sources in particular, such as the magnetron, suffer from lack of frequency stability due to temperature and pulse repetition frequency (PRF) changes. For high power microwave applications, e.g. 0.5 kiloWatts (0.5 kW) and above, it has been especially uneconomical and impractical to provide for frequency stabilization.
Techniques for frequency stabilization generally utilize high Q cavity stabilization, phase locked loops, or injection locking. High Q cavity stabilization is typically very expensive and difficult to implement due to the size and complexity of required microwave cavities. Such cavities generally also have an inherent insertion loss resulting in an undesirable reduction in power. Phase locked loops represent the most costly and technically complex method, and involve the greatest number of components and highest area requirements. Injection locking can tend to be complex and expensive because of size requirements, and requires power consumption. A stable active source to provide a frequency reference is also typically required. A significant drawback of injection locking has been a limitation on the radio frequency (RF) output power to be injection phase locked. Generally, only expensive apparatus such as a large number of power field effect transistors (FETs) have been available to provide the injection locking reference source for high power injection locking.
Thus, what is needed is a practical, economical method for frequency stabilization of high power electromagnetic sources, particularly microwave generating sources, with the method preferably employing passive means.